This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are requesting beam time to further four projects. First we are continuing our studies on nitrosylated heme proteins, including the nitrophorins and other heme-based NO signaling proteins. Second, we have undertaken a wide-ranging study of protein S-nitrosation in NO signaling, including S-NO formation (thioredoxin, myoglobin), and control of glutathione S-nitrosation by the protein GSNO reductase. These studies include a drug discovery component. Third, we are investigating proteins involved in riboflavin synthesis in S. coleicolor, particularly the GTP cyclohydrolase II family. Fourth, we are pursuing reaction intermediates in several proteins, including the multicopper oxidase CueO. Synchrotron radiation is needed for: (1) MAD structure determination;(2) Sufficient resolution to determine accurate geometry of SNO adducts, define heme distortion from planarity, model multiple conformations;and determine the structure of freeze-trapped intermediates in active crystals;(3) Variable x-ray wavelengths can be used to minimize photoreduction of iron-heme centers.